Clamping circuit and method for DMOS drivers

• US 6,798,271 B2
• Filed: 04/04/2003
• Issued: 09/28/2004
• Est. Priority Date: 11/18/2002
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Swize, Gregory Emil
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): Nguyen, Hai L.
• Application Number:
  US10/249,398
• Publication Number:
  US 20040095183A1
• Time in Patent Office: 543 Days
• Field of Search: 327/423, 327/424, 327/427, 327/448, 327/508, 327/587, 327/588, 327/109, 327/110, 327/507, 360/46, 360/67, 360/68, 363/58, 363/63
• US Class Current: 327/424
• CPC Class Codes: H03K 17/08142 in field-effect transistor switches
• CPC Class Codes: H03K 17/6872 using complementary field-effect transistors

Abstract

A transconductance circuit (16) and method for protecting an H-bridge power circuit (10) that provides power to a load that includes an inductive component (14) connected between one side of the inductive component (14) and a gate (25) of a low side transistor (24) of the H-bridge (10). The transconductance circuit (16) operates to pull current from the inductive component (14) to ground (30) when the inductive load (14) sources current to a body diode of the high side transistor (20). The transconductance circuit (16) creates a regulated voltage to the gate (25) of the low side transistor (24) to cause the low side transistor (24) to conduct the current away in a regulated manner from the inductor (14) and the high side transistor (20) to ground (30).

Claims

1. In an electrical circuit including an inductive load which has a first side driven by an FET pair including a high side transistor connected in series with a low side transistor between a supply voltage and a reference potential, wherein a second side of said inductive load is connected to a current carrying circuit capable of carrying current to a reference potential, and wherein said high side transistor has an associated body diode, a circuit comprising:

circuitry to operate said high side transistor and said current carrying circuit capable of carrying current to selectively allow a current to flow from said supply voltage through said high side transistor, said inductor, and said circuit capable of carrying current; and

a transconductance circuit loop including a transconductance circuit connected to control said current carrying circuit capable of carrying current to pull current from said inductive load to said reference potential when said inductive load sources current to said body diode sufficient to cause the voltage across said body diode to exceed a predetermined trip voltage.

2. The circuit of claim 1 wherein said current carrying circuit capable of carrying current includes a second low side transistor and wherein said transconductance loop creates a regulated voltage to a gate of said second low side transistor to cause said second low side transistor to regulatedly conduct said current away from said inductor and said high side transistor to said reference potential.

3. In an electrical circuit including an inductive load which has a first side driven by an FET pair including a high side transistor connected in series with a low side transistor between a supply voltage and a reference potential, wherein a second side of said inductive load is connected to a current carrying circuit capable of carrying current to a reference potential, and wherein said high side transistor has an associated body diode, a circuit comprising:

circuitry to operate said high side transistor and said current carrying circuit capable of carrying current to selectively allow a current to flow from said supply voltage through said high side transistor, said inductor, and said circuit capable of carrying current; and

a transconductance circuit loop connected to control said current carrying circuit capable of carrying current to pull current from said inductive load to said reference potential when said inductive load sources current to said body diode sufficient to cause the voltage across said body diode to exceed a predetermined trio voltage,

wherein said transconductance loop comprises;

a sense circuit connected to sense a voltage on a node between said high side transistor and said low side transistor to provide a sensed voltage;

a compare circuit connected to compare said trip voltage with the sensed voltage to provide an output current to a control element of said circuit capable of carrying current to cause said current carrying circuit capable of carrying current to conduct amount of current related to a magnitude of said sensed voltage over said trip voltage.

4. The circuit of claim 3 wherein said compare circuit comprises a pair of FET compare devices having interconnected gates connected to said trip voltage, wherein said FET compare devices conduct when said sensed voltage exceeds said trip voltage plus a gate to source voltage drop on one of said FET compare devices.

5. The circuit of claim 4 further comprising a sinking circuit for sinking a constant current from a gate of said low side driver transistor.

6. A circuit for protecting upper transistors of an H-bridge circuit that provides power to a load that has an inductive component, comprising:

a transconductance circuit loop including a transconductance circuit connected between one side of said inductive component and a gate of a low side transistor of said H-bridge,

said transconductance circuit operating to pull current from said inductive component to ground when said inductive load sources current to a body diode of said high side transistor.

7. The circuit of claim 6 wherein said transconductance loop creates a regulated voltage to said gate of said low side transistor to cause said low side transistor to regulatedly conduct said current away from said inductor and said high side transistor to ground.

8. A circuit for protecting upper transistors of an H-bridge circuit that provides power to a load that has an inductive component, comprising:

a transconductance circuit loop connected between one side of said inductive component and a gate of a low side transistor of said H-bridge,

said transconductance circuit operating to pull current from said inductive component to ground when said inductive load sources current to a body diode of said high side transistor,

wherein said transconductance loop further comprises;

a sense circuit connected to sense a voltage on a node between said high side driver and said low side driver to provide a sensed voltage;

a compare circuit connected to compare a trip voltage with said sensed voltage to provide an output current to a control element of said low side transistor to cause said low side transistor to conduct amount of current related to a magnitude of said sensed voltage over said trip voltage.

9. The circuit of claim 8 wherein said compare circuit comprises a pair of FET compare devices having interconnected bases connected to a trip voltage, wherein said FET compare devices of said compare circuit conduct when said sensed voltage exceeds said trip voltage plus a gate to drain voltage drop on one of said FET compare devices.

10. The circuit of claim 9 further comprising a sinking circuit for sinking a constant current from a gate of said low side driver transistor.